This invention relates to a continuous process for controlled hydrolysis of corn grit and to a product obtained therefrom.
Kernels of corn contain naturally occurring starch, a polysaccharide constituted, in part, by amylose and amylopectin moieties. Upon heating under hydrolyzing conditions, these moieties deploymerize. This depolymerization is called gelatinization. When naturally occurring starch undergoes gelatinization, it tends to form a colloidal suspension in water that gels upon cooling. Starch that is partially or fully gelatinized is useful as a binder in various pelletization applications, e.g., iron ore pelletization, fertilizer pelletization, and the like, either alone or in combination with other polymeric materials.
Gelatinization of corn starch by heating whole kernels of corn is a lengthy process that is not cost efficient. A long time period is required for water to penetrate the pericarp or hull of the corn kernel.
Whole kernels of corn, or ground corn that has not been degerminated, contain floury endosperm and horny endosperm (also known as corn grit). Each type of endosperm, when cooked, ruptures and releases gelatinized starch at different rates. Because these two types of endosperm contribute gelatinized starch at different rates, it is difficult to control the amount of gelatinized starch that will be produced. If the corn particles are cooked long enough to have the horny endosperm contribute a significant portion of the overall gelatinized starch content of the ultimately produced corn flour, then the earlier released starch from the floury endosperm is over-gelatinized. If, however, the corn particles are cooked for a time period that does not result in the over-gelatinization of the starch from the floury endosperm, then the horny endosperm typically does not contribute enough gelatinized starch to the flour and is underutilized. As a result, product uniformity and quality assurance are difficult to achieve.
Yet another problem associated with the previously known processes for cooking whole kernels of corn is that this typically cannot be accomplished in a continuous process. Instead, batch processes are used, because it takes a relatively long time period to hydrate whole kernels of corn. Batch processes require the use of more than one production line, or a large number of holding tanks in which to hydrate the whole kernels of corn. Therefore, it would be desirable to use a continuous process because it requires a single production line and fewer pieces of equipment, which is a less costly process expedient than a batch process. The present invention satisfies this desire.
Corn collets having a basic pH value are produced in a continuous process by first conditioning corn grit (horny endosperm) at atmospheric pressure and at elevated temperature (about 180xc2x0 F. to about 200xc2x0 F.) with an aqueous sodium hydroxide solution in the presence of steam, and while maintaining a corn grit moisture content of no more than about 15 weight percent, preferably about 14 weight percent. The conditioning is carried out for a time period sufficient to partially gelatinize the corn grit to a gelatinization level in the range of about 5% to about 25%.
The partially gelatinized corn grit is then passed through an extruder at a superatmospheric pressure (usually about 1.1 atm to about 1.5 atm) and a temperature in the range of about 150xc2x0 F. to about 210xc2x0 F. while the corn grit moisture content is maintained in the range of about 20 to about 25 weight percent, preferably about 22 weight percent. Cooked corn grit in the form of corn collets are discharged from the extruder at an exit temperature in the range of about 200xc2x0 F. to about 215xc2x0 F. and at a moisture content in the range of about 9 to about 12 weight percent.
The corn collets are subsequently cooled to ambient temperature and dried to a moisture content of no more than about 9 weight percent, preferably below 9 weight percent.
If desired, the cooled and dried corn collets can be comminuted to a meal or flour, preferably a flour passing through a 100-mesh screen, U.S. Sieve Series.